The invention refers to a method of making a natural sweetener based on Stevia rebaudiana, and use thereof.
As set forth in the article entitled "Stevioside", page 295 to 307 by Abraham I. Bakal and Lyn O'Brien Nabors in the publication "Alternative Sweeteners", Marcel Dekker Inc., New York 1986 as well as in the various citations referred to in that article, the plant Stevia rebaudiana is native in South America and is used as traditional sweetener for mate tea. The components of this plant are characterized by a high sweetness intensity so that tests were undertaken to cultivate this plant not only in its native countries but also in East Asia and to commercially exploit extracts obtained therefrom. The sweetness of the plant parts and of the extracts obtained therefrom can be attributed to a number of chemical substances which all belong to the class of diterpene glycosides. The most important singular compounds are the stevioside and rebaudiside A which have the following chemical structure: ##STR1##
Aside from these two compounds, further compounds could be identified which contribute to the sweetness intensity.
In order to make sweeteners from Stevia rebaudiana, the plant parts, usually the dried leaves, are extracted with water or with an organic solvent such as alcohol. The extracts are then subjected to various refining steps for purifying and enrichment of the components effecting the sweetness intensity. These refining steps may encompass the following process types: precipitation of contaminants by means of inorganic salts and subsequent treatment of the extract with ion-exchangers, precipitation of the contaminations through controlled variation of the pH value, precipitation of undesired accompanying substances through aggregation on polymers or fixed adsorbents, purification through chromatographic steps, purification through adsorption on pigments; liquid extraction; electrophoresis, membrane filtration.
The number of publications cited in Chemical Abstracts volumes 85-105, which primarily are published Japanese patent applications, is above 70. Products which are obtained from raw extracts and have improved sweetness intensity are also disclosed for example in the U.S. Pat. Nos. 4,082,858 and 4,219,571, with the latter patent specification referring to an enzymatic production method.
The sweetness intensity of the extract, which sometimes is simply called "stevioside", is usually about 150 to 300 times the sweetness intensity of sucrose depending on the used concentration.
The reason that kept sweeteners derived from Stevia rebaudiana from being introduced in Europe and North America is a bitter and astringent aftertaste which frequently is also described as menthol-like. In all known, commercially applicable methods, this aftertaste remains in the extract and leaves a greatly impaired taste, especially at high purity of the extract or at high concentration. Although such taste or aftertaste has been tolerated in countries in which sweeteners based on Stevia rebaudiana are used in foodstuffs and beverages, a product of such quality would not be accepted by consumers in Europe or North America. Further, the bitter aftertaste also limits the application of sweeteners of Stevia rebaudiana for use in alcohol-free beverages such as soft drinks.